| Summary: | Faculty of Science
School of Geography And Archaeology and Enviromental Studies
9905693x
Nicola@crg.bpb.wits.ac.za === The Cape Town brown haze is a brown-coloured smog that is present over the Cape
Town atmosphere during the winter months due to the accumulation of gaseous and
particulate pollutants. The main aim of this research was to evaluate the impact of
atmospheric pollutants to visibility impairment by the brown haze through visibility
modelling of major pollution sources around the City of Cape Town. The screening
model, VISCREEN, the Plume Visibility model, PLUVUE II and the CALPUFF
Modelling System were employed to model the visual impact of emissions from the
major sources. Two point sources, Caltex Oil Refinery and Consol Glass, and three
area sources, Cape Town Central Business District (CBD), Cape Town International
Airport and the townships of Khayelitsha and Mitchell’s Plain were identified as the
major sources. An initial screening analysis indicated that emissions from the two
industrial sources would be visible and would result in a yellow-brown discolouration
of the atmosphere. Detailed modelling using PLUVUE II identified the area sources
of Cape Town CBD and the townships to be the significant contributors to visibility
impairment over Cape Town. Plume perceptibility is primarily dependant upon
particulate emissions while NOx emissions influence the colouration of the
atmosphere. CALPUFF was employed to assess the distribution of NOx, SO2 and
PM10 concentrations over the area and the associated visibility impairment on a nonhaze
(13 August 2003) and haze day (22 August 2003). Pollutant concentrations were
considerably reduced on the non-haze day compared to the haze day. The Cape Town
CBD was an important source of all the major pollutants with the townships
contributing significantly to the aerosol loading over Cape Town. Pollutant
concentrations are particularly elevated during the late evening and early morning
periods, particularly between 7 am and 8 am. Visibility impairment is greatest on the
haze day, particularly over the central Cape Town region and the townships. The
greatest reduction in visibility is experienced between midnight and 9 am which
corresponds with the periods of elevated atmospheric pollutant concentrations.
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